Formidilosus, energy is what is needed, in the first place, to get the work of penetrating and destroying tissue done.
It comes from velocity (and mass) so saying that energy/velocity is required is, basically, quite correct, in my opinion.
The thing is that being necessary, it is not enough, so yes, you need a bullet of the proper construction offering a good balance of expansion and penetration.
And yes, you need to place it properly. In my opinion, as all bullets carry some energy/velocity, and all of them are capable of some kind of expansion and penetration, bullet placement is most important, there being no substitute for a well placed shot.
Saludos,
Alvaro
